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Caddisflies

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Caddisfly larva (Brachycentrus lateralis).

Photo: Claude Pilon

Caddisflies (Trichoptera) or shadflies being eaten by a bird.

Photo: André Sarrazin

Tabs group

Description

Caddisflies look very much like small moths. Depending on the species, they range from 4 mm to 4 cm in length. They have long slender antennae and vestigial mouthparts that enable them to ingest liquid food only.

Two pairs of dark membranous wings, which are folded roof-like over the abdomen when at rest, are located on the thorax. The wings are covered with tiny hairs that give them a downy look.

The cylindrical abdomen usually tapers off to a pair of appendages in females and to at least two pairs in males.

Life cycle

Caddisflies may mate on the ground or on vegetation. The eggs are generally enclosed in a gelatinous mass and laid as a long string, ball or ring in the water, on plants or under stones. Most of the time, the eggs will hatch a few days after being laid.

With few exceptions, the larvae are aquatic. Most larvae produce silk and can be divided into three groups:

Those that make a case, and are also called purse-case or tube-case makers

Those that spin a silk net, and are also called net-spinners

Those that don’t build a net or case, and are free-living forms

Larvae take a little under one year to grow and undergo four moults. The end of the larval stage signals the start of the pupal stage, when the larva spins a cocoon. This stage lasts around three weeks, after which the insect cuts through its case and swims to the surface.

The fully formed adult emerges when the larva reaches the surface or climbs onto a solid surface. Adult caddisflies are ready to mate and immediately search for a partner. Adults live from one week to about two months.

Caddisflies have a single generation per year, but the length of their life cycle varies according to the species.

Habitat

Caddisfly larvae are typically found at the bottom of nearly all freshwater habitats. Adults usually remain in the area where they emerged.

Did you know?

Interesting facts

Seeing a pile of twigs or dead leaves moving at the bottom of a pond is usually a sign of a larva dragging its case; as it travels, only the front part of the body sticks out from the protective case. The larvae carry their cases using a pair of hooks at the tip of the abdomen.

To build their cases, larvae use the silk they produce and materials from their surroundings: decomposing leaf litter, twigs, grains of sand, tiny shells, etc. Examining the case can provide clues to help identify the caddisfly family, and sometimes even the genus.

Ecological roles

Caddisfly larvae play a vital role as a significant food source in freshwater ecosystems for fish, birds and other aquatic predators. As adults, they are eaten by a variety of animals.

Larvae are used as environmental indicators; different species are sensitive to various types of pollution.